Q1: Pick up the correct statement from the following :

ANS:D - All the above.

1. In treated sewage, 4 ppm of D.O. is essential: This statement is not universally true. The required level of Dissolved Oxygen (D.O.) in treated sewage depends on various factors such as environmental regulations, the treatment process employed, and the receiving water body's characteristics. While some regulations or guidelines may specify a target D.O. level, it is not always set at 4 ppm. The optimal D.O. level may vary depending on the specific circumstances and the intended use of the treated sewage.
2. Only very fresh sewage contains some dissolved oxygen: This statement is generally true. When sewage is initially discharged into a water body, it may contain some dissolved oxygen (D.O.) due to aeration or mixing with oxygenated water. However, as sewage undergoes biological decomposition and microbial activity, the dissolved oxygen levels tend to decrease rapidly. In older or more stagnant sewage, the dissolved oxygen levels may become very low or even depleted entirely.
3. The solubility of oxygen in sewage is 95% that is in distilled water: This statement is generally false. Sewage contains various organic and inorganic substances that can affect the solubility of oxygen. The presence of organic matter, nutrients, and other substances in sewage may decrease the solubility of oxygen compared to distilled water. The actual solubility of oxygen in sewage can vary depending on factors such as temperature, pressure, and the composition of the sewage.